1. Field of the Invention
This invention relates to a process for preparing crystalline zeolitic materials from organic diamines. More particularly, this invention relates to an improved process for preparing crystalline zeolite materials of the ZSM-4 type from a reaction mixture containing triethylenediamine.
2. Description of Prior Art
Zeolitic materials, both natural and synthetic, have been demonstrated in the past to have catalytic activity for various types of hydrocarbon conversion reactions, particularly for catalytic cracking. Some of these zeolitic materials comprise ordered, porous crystalline aluminosilicates having a definite crystalline structure, as determined by X-ray diffraction, which contain a large number of small cavities interconnected by a series of still smaller channels or pores. These cavities or pores are precisely uniform in size for a given zeolitic material. Since the size of these pores is such that they adsorb molecules of certain dimensions, while reject those of larger dimensions, these materials are known in the art as "molecular sieves" and are utilized in a variety of processes which take advantage of the selectively adsorptive properties of these materials.
These zeolitic molecular sieves include a variety of positive ion-containing crystalline aluminosilicates, both natural and synthetic. Such aluminosilicates are generally described as having a rigid three-dimensional network of SiO.sub.4 and AlO.sub.4 tetrahedra in which the tetrahydra are cross-linked by the sharing of oxygen atoms whereby the ratio of the total aluminum and silicon atoms to oxygen atoms is 1:2. The electrovalence of the tetrahydra containing aluminum is negatively charged and the composition is balanced by the inclusion in the crystal structure of a cation, for example an alkali metal or an alkaline earth metal cation. Thus, e.g., a univalent positive sodium cation balances one negatively charged aluminosilicate tetrahydra. Conversely, if an alkaline earth metal cation, e.g., calcium or strontium, is employed in the crystal structure of an aluminosilicate, it balances two negatively charged aluminosilicate tetrahydra due to its doubly positive valance. Some compositions of the aluminosilicate family can contain both double positive cations, e.g., calcium, and univalent positive cations, e.g., sodium, and can be prepared in a conventional manner by base exchanging a sodium aluminosilicate with a calcium compound solution in such a manner that not all of the sodium ions are removed. Such cation exchange enables those skilled in the art to vary the size of the pores in a given aluminosilicate by suitable selection of the particular cation. The spaces between the tetrahydra are usually occupied by molecules of water prior to dehydration.
One of the crystalline zeolites known in the art is identified as ZSM-4. The ZSM-4 zeolite is usually employed for the isomerization and disproportionation of aromatic hydrocarbons. This particular catalyst has been found to be exceptionally selective in the isomerization of aromatics, such as xylene, or the disproportionation of alkylbenzenes, such as toluene. It is known that the ZSM-4 zeolite will form only if the reaction mixture contains a source of an organic nitrogen. More particularly, it was believed in the prior art that ZSM-4 can be produced only in the presence of tetramethylammonium cations, as described by J. Ciric in U.S. Pat. No. 3,923,639 and by Bowes et al, in U.S. Pat. No. 3,578,723. (The entire contents of both of these patents are incorporated herein by reference). The source of an organic cation used in an Omega zeolite catalyst, a catalyst analogous to the ZSM-4 zeolite, was more broadly expanded to include ammonium and alkyl-ammonium groups, as described by Flanigen et.al., in Belgian Pat. No. 702,248. In a more recent advancement in the art, Rubin, et. al., in U.S. Pat. No. 4,021,447 showed that choline chloride and pyrrolidine could also be used as sources of organic cations in the ZSM-4 synthesis.
Thus, the prior art processes producing the ZSM-4 zeolite or zeolites similar thereto have been limited to the use of tetramethylammonium cations or amines containing one nitrogen atom. The use of DABCO has not heretofore been contemplated in the synthesis of ZSM-4 zeolites or zeolites whose physical and/or chemical characteristics are similar to those of ZSM-4.
Accordingly, it is the primary object of the present invention to provide a process for the production of a ZMS-4 type crystalline zeolitic material, whose composition and physical and/or chemical characteristics are essentially those of ZSM-4, wherein a DABCO is used in the synthesis thereof.
Additional objects of this invention will become apparent to those skilled in the art from the study of the specification and of the appended claims.